I’ll give you three guesses, but you’ll only need one …
The vast majority of the infected were unvaccinated against the disease, including kids who were too young for the shots and anti-vaxxers who chose against them. That’s how you get an outbreak. But six of the cases got their measles-mumps-rubella vaccine—the MMR shot—and still managed to get infected. And all but two of them had gotten at least two doses, the standard recommendation.
So what happened?